Being organic materials which are stable and can be industrially produced, plastics have been used in various applications.
In particular, among plastics, so-called “engineering plastics”, have excellent properties such as mechanical strength or heat resistance, in contrast to general plastics such as polyethylene or polystyrene, and so can be used in place of metallic materials. In recent years, engineering plastics have been put into practice in various industrial fields, being excellent functional materials. Among engineering plastics, polyamide, polyethylene terephthalate, polycarbonate, polyacetal, polyphenylene ether and the like are called “general purpose engineering plastics”, and are able to provide reasonable performance and are inexpensive, and accordingly, are used in large quantities in industry.
Other than the general purpose engineering plastics, plastics having exceptional mechanical strength or heat resistance are called “special engineering plastics” or “super engineering plastics”, and application thereof is limited due to cost or formability thereof.
Examples of the special engineering plastic include polyimides, polysulfones, all-aromatic polyesters, crystalline polyesters, polyketones, cyanates, polyphenylenesulfides, and the like.
Among engineering plastics, polyketone is a polymer having a ketone group in its main chain. Main examples of polyketone include polyether ketone (hereinafter, abbreviated as PEK), polyether ether ketone (hereinafter, abbreviated as PEEK), polyether ketone (hereinafter, abbreviated as PEKK), and polyallyl ether ketone or aliphatic polyketone composites thereof.
Polyallylether ketone is a heat-resistant polymer which can be injection molded. The ratio of rigid ketone groups to flexible ether bonding is a factor which determines the heat resistance of the polymer. Further, PEK or PEEK, having a high ratio of ketone groups, have high heat resistance. Thermal deformation temperatures of PEK and PEEK range from about 300° C. to about 350° C., and continuous duty temperatures thereof range from about 200° C. to about 260° C., and among thermal plastics, PEK and PEEK exhibit the best heat resistance. PEEK has a melting point of 334° C., and exhibits high resistance to hydrolysis, high chemical resistance, high radiation resistance, and fire resistance, and accordingly, is used in air planes, the field of atomic power generation, electronics such as computers, cable-coating materials, connectors, parts surrounding the engine in automobiles, and a hydrothermal-pump housing and the like. Heat resistance, chemical resistance, fire resistance, and radiation resistance of PEK are higher than those of PEEK, and PEK is used in atomic power generation and air plane-associated parts.
However, since these engineering plastics use expensive monomers as raw materials, there is little room for cost reduction, thus it is not expected that a large market for them will develop in the future.
Condensation based engineering plastics containing aromatic rings in their main chains have conventionally been synthesized by condensation reactions between two functional groups. However, in recent years, new synthesizing methods in which large ring compounds are polymerized by ring-opening or they are directly polymerized by dehydrogenation have been reported.
Further, attention has been drawn to polyketones which do not contain an aromatic ring in their molecules, which are so-called aliphatic polyketones. An aliphatic polyketone (“CALIRON”(trade name)), which is a special engineering plastic developed and manufactured by Shell Oil Co., Ltd., does not contain an aromatic ring in its molecule and can be manufactured from inexpensive raw materials such as olefin such as ethylene and CO, hence a wide range of applications can be expected. Examples of applications of aliphatic polyketones include packaging, containers, electric materials, electronic components, automobile materials, building materials, gears, sliding parts, adhesives, and fibers, and aliphatic polyketones are of interest in these industrial fields.
At present, aliphatic polyketones are mainly synthesized by a method in which an olefin, such as ethylene or propylene, and carbon monoxide are copolymerized by using a metal complex such as palladium, nickel or cobalt, as a catalyst (see U.S. Pat. No. 4,835,250 for example).
However, at present, the synthesis of these metal complexes is extremely difficult. For instance, C. Bianchini, et. al., Marcromolecules 32, pp. 4183-4193 (1999) discloses a synthesis method of a palladium complex. However, since the disclosed synthesis has the problem of requiring conduction of a complicated reaction process comprising 5 steps or more, methods of synthesizing stable aliphatic polyketones in this way are still at a developing stage.
At present there has been no report of an example of a synthesis of an aliphatic polymer having a ketone group and ether bonding in its main chain, such as aliphatic polyether ketone or aliphatic polyether ether ketone, an aliphatic polyketone for which a wide range of applications is expected.